Process of teating cold rolled straight chrome type stainless steel



Patented Aug. 5, 1952 OFFICE raocsss F TREATINGCOLD ROLLED STRAIGHT CHROME TYPE- STAINLESS STEEL,

Joseph C; Kientzj Jn, Carnegie, Pa., assignor to SuperionSteel Corporation, Pittsburgh, Pa., a a

corporation of Virginia Y v No Drawing.

This invention relates to the treatment'of cold rolled straight chrome type stainless steel and particularly to the annealing and pickling of such steel. It relates more particularly to a process of treating cold rolled straight chrome type stainless steel which makes feasible the batch annealing of such steel, as, for example, between cold reduction steps.

In the production of cold rolled straight chrome type stainless steel it is customary to cold roll hot rolled strip with intermediate continuous annealing and pickling steps. For example, if cold rolled straight chrome type stainless steel .018 inch in thickness is desired a customary ay of producing such steel is to cold roll hot rolled strip .125 inch thick to about .060 inch in thickness, continuously anneal and pickle, then cold roll to about .032 inch in thickness, then again continuously anneal and pickle, then cold roll to final thickness andthen for a third time continuously anneal and pickle. The continuous annealing and pickling steps are desirable because the oxide formed during annealing in that fashion is removable by pickling with the ordinary commerand pickling equipment. I have discovered that.

with a particular after treatment it is possible to substitute a batch anneal for the conventional continuous anneal.

It has heretofore been considered not feasible to batch anneal cold rolled straight chrome'type stainless steel becausewhen such steel is batch annealed there is formed thereon a film of oxide not satisfactorily removable by commercial pickling acids. The oxide is a tenacious chromic ox.- ide whichais insoluble in acids ordinarily used for-commercial pickling such as sulphuric and nitric-hydrofluoric acids- While-this chromicoxide film can be dissolved if the steel is treated by a special caustic reagent such, for example, as sodium hydride or molten sodium hydroxide containing an oxidizing agent prior to its treatment with acid, use of those reagents requires special equipment and is otherwise undesirable.

I have discovered that cold rolled straight chrome type stainless steel can be satisfactorily Application February 21,1947, Serial No. 730,195"

6 Claims. (01. 134 -3) produced on a commercial scale by substituting a batch anneal for the conventional continuous anneal if the steel is subjected to a treatment following the batch anneal and prior to the subsequent pickling treatment to fracture the tenacious oxide which is formed during the batch an' neal. I find that if that oxide is fractured or cracked it is thereby rendered removable by the usual commercial pickling acids, e. g., by pickling successively in sulphuric and nitric-hydrofluoric acids. Apparently the pickling acids find their way through the fractures or cracks in the oxide film and by action at the contiguous surfaces of the steel and the oxide film partially dissolve the Y film and cause the undissolved portion to become separated from the steel. The undissolved film' drops off in small pieces and settles at the bottom of the Pickling tank from which it may be cleaned out.

The fracturing or cracking of the tenacious chromic oxide film formed by the batch annealing of cold rolled straight chrome type stainless steel may be effected by stretching the steel whereby to cause fracturing of the relatively unelastic film. I find it desirable to stretch the steel by cold rolling it. Only a single very light skin pass in a cold rolling mill is necessary to cause sufficient fracture or rupture of the oxide film to permit its effective removal by the ordinary commercial pickling acids. gauge of the order of one or two thousands of an inch or less in very thin cold rolled straight chrome type stainless steel is ordinarily sufiicient to effectively fracture the oxide film. It is preferablethatthe steel be subjected to the light skin pass when it is in dry condition.

The cold rolled straight chrome type stainless steels to which my invention is applicable are those containing chromium in about the range 10-30% and not containing a substantial percentage of nickel. Ordinarily such steels will contain. carbon in about the range .011.2%. An

example of a steel to which my invention isapplicable is:

As an illustration of a procedure according to my invention for the production of cold rolled A reduction in 3 straight chronic type stainless steel, I may hot roll a billet of straight chrome type strainless steel to about .125 inch in thickness, batch anneal and pickle in the usual way for hot rolled strip, cold roll togabout .060 inch in thickness, batch anneal, skin .pass in a cold rolling'mill (reducing the gauge say .002 inch), pickle successively in sulphuric acid and nitric-hydrofluoric acid, cold I roll to about .032 inch in thickness, batch anneal, skin pass in a cold rolling mill'ireducingthe gauge say .002 inch), pickle successively-insulphuric acid and nitric-hydrofluoric acid, cold roll to about .018 inch in thickness,batchannealskin pass in a cold rolling mill (reducing .tthegauge. say .001 inch) and pickle successively in sulphuric acid and nitric-hydrofluoric acid. The steel may be pickled either in the coil or continuously or after shearing into relatively short lengths. tions of the coil should be slightly separated to permit, adequate ingressiof :the pickling acids. .I prefer to;pickle the-steelwcontinuously. This may be; done either as .a combined :contir uous operan th thecoicim iins step a d mmedi te ow n "thed r l n or as a-sena ep. e i6 Q "QQild :follDW D (p. 1 l ins and. then tu ncoi-led ,prior pickling. In pickling the t e s pre rably treated cce s t phuricyaciol; and nitric-hydrofluoric acid.

sm e-explain d. t id fi mc a i sstep enablesthe ordinary commercialpieklingacids to effectively remove the tenacious .chromic :oxide lmr e me n: hee ldm ifi r g b e vp stainless steel -batch annealing, rendering unnecessary theuse :of caustic reagents and the equipment needed -for treatment therewith.

I have described .a presentpifeferred methodof practicing the invention it is to be distinctly understood that the invention is not lim-. ited thereto. but may be otherwise variously practiced-within thescope of the following claims.

.1. In the. treatment of cold rolledstraight chrome type stainless steelcontaining chromium in, about the range ..IOQ30.% which has 1i ormed thereon .a film-of oxide such as .is termed by batch annealing and'which is nctsatisiactorily removable byipickling successively sulphuric and nitrichydrof luoric.acids the-steps of stretching the steel by coldrollirigit, thereby'fomnin-g crackslinsaid film, and pickling .thesteel suc cessively Fin sulphuric land nitric-hydrofluoric acids which fatter the first .mentioned step-is efiective' for satisfactorily-removing the '2.'.In. the. treatment of cold rolled straight chrome type stainlesssteel containing chromium in about. the range .LU,-3D% which has vformed thereon a film of oxide .such as is formed bybatchann ealing and which is .not satisfactorily removable by pickling successivelyin sulphuric n ric-h dro uoric acid the ps orm:

ns r c s. sa d fi m. b s e ch n t e s e 3. In.v the. treatment. .Qt cbm...m11e& straight hro tyne St inless. steel containing. chromium.

4 in about the range 10-30% which has formed thereon a film of oxide such as is formed by batch annealing and which is not satisfactorily removable by pickling successively in sulphuric and nitric-hydrofluoric acids, the steps of subjecting the steel to a light skin reducing passxin a cold rolling mill, thereby forming cracks in said film, and pickling the steel successively in sulphuric and nitric-hydrofluoric acids which after the first mentioned-stcpiisefiective for satisfactorily re- 4. In the treatment of cold rolled straight tchrome type stainless steel containing chromium :in aboutrfiheirange 10-30% which has formed thereona iil'm dfoxide such as is formed by batch annealing and which is not satisfactorily removable .by pickling successively in sulphuric and If it is pickled in the coil the convoluthe'r'steel by cold rolling it, thereby forming cracks in said film, and continuously with said cold rolling-pickling, thesteelsuccessively in sulphuric and nitric=hydrotluoric acids which after the first, mentioned step is effective .for satisfactorily .re-. o i s' e film.

I the rea me t of ol r l e ai ht qh m t e s emli sst e c ntai i h omium in about the range 40-30% which has formed thereon a film of oxide such as .is-forifnedby batch annealing and which isnot-s a.tis1-:actor-ilyremovable by pickling successively .in sulphuric nitric-hydrofluoric acids, the-steps of stretchingv the steelby coldrollinggit, thereby fior-mingrcracks in said fi1m,; CQi1-ll'lg thesteel aftersaid coldrolling -and thereafter uncoilingand continuously pickling the .steel successively in sulphuric and nitric-hydrofluoric acids which after the first mentioned step is eifective fo r satisfactorily removingthe film. 7 g 7 6.1111 the treatment of cold rolled straight ie-s i s stee i isins h mzism. in about the .range .1 ).30, which hes formed thereonafilm ofoxide such as is iior-medby batch annealing.a 'nd irzh'ich .is .not satisfactorily-Emm able by pickling successively in sulphuric and nitric-hydrofluoric acids, the steps of forming crack's in said iby. stretching the steel and picklingfsuccessivel'y in sulphuricand nitric-bye drofiuo r'ic acids'the steel in coil form-with tl-ie contractionsof the coil slightly separated to permitiireelaccess ofthepickling acid, which pickling after the first mentioned step-is .eifecti ve for satisfactorily removingflthefilmf JOSEPH (3-. KIE-NTZ, JR.

REF-E-RENCES CITED The renewing references-are of record-inthe Date- 7 Number. Name acacia *nempsterzze;when- Jim; 28, -1-90-8 .igeaamao: Marsh :oct. 4;1321 assume. Ha s-spun -Dec. ,11925: mes es: FNaug-le aunc c s iseo pea-7.15s. Fellows Dec.- 15193 1 2340mm ct Feb. 1; i944 Been a I 

1. IN THE TREATMENT OF COLD ROLLED STRAIGHT CHROMINE TYPE STAINLESS STEEL CONTAINING CHROMIUM IN ABOUT THE RANGE 10-30% WHICH HAS FORMED THEREON A FILM OF OXIDE SUCH AS IS FORMED BY BATCH ANNEALING AND WHICH IS NOT SATISFACTORILY REMOVABLE BY PICKLING SUCCESSIVELY IN SULPHURIC AND NITRIC-HYDROFLUORIC ACIDS, THE STEPS OF STRETCHING THE STEEL BY COLD ROLLING IT, THEREBY FORMING CRACKS IN SAID FILM, AND PICKLING THE STEEL SUCCESSIVELY IN SULPHURIC AND NITRIC-HYDROFLUORIC ACIDS WHICH AFTER THE FIRST MENTIONED STEP IS EFFECTIVE FOR SATISFACTORILY REMOVING THE FILM. 